The invention is based on a method for metering a reagent into an exhaust gas duct and on a device for carrying out the method.
The present invention also relates to a computer program and to a computer program product.
Laid-open application DE 101 39 142 A1 describes an exhaust gas treatment device of an internal combustion engine, in which, in order to reduce the nitrogen oxide emissions, use is made of an SCR catalytic converter (Selective-Catalytic-Reduction) which reduces the nitrogen oxides contained in the exhaust gas to nitrogen using the reducing agent ammonia. The ammonia is obtained from a urea-water solution in a hydrolysis catalytic converter arranged upstream of the SCR catalytic converter. The hydrolysis catalytic converter converts the urea contained in the urea-water solution with water to form ammonia and carbon dioxide. The urea-water solution is brought by a pump to a predetermined pressure. A metering valve defines a predetermined volumetric flow rate. Compressed air is mixed with the urea-water solution in a mixing chamber. The urea-water solution is sprayed together with the added air by means of a spray tube into the exhaust gas of the internal combustion engine in such a manner that the flow approaching the SCR catalytic converter is as uniform as possible.
Laid-open application DE 10 2004 018 221 A1 describes a method of the type in question and a device of the type in question, in which method and device a pressurized reagent is likewise sprayed into the exhaust gas of an internal combustion engine upstream of an SCR catalytic converter. The reagent pressure is fixed to a predetermined desired reagent pressure depending on a characteristic variable. An operating variable of the internal combustion engine and/or a characteristic variable of the exhaust gas of the internal combustion engine can be used as the characteristic variable. The predetermined desired value of the reagent pressure is controlled within the scope of a closed loop control, in which the actual reagent pressure is detected by a reagent pressure sensor. Compressed air can be added to the reagent. The compressed air pressure can likewise be controlled to a predetermined desired value of the compressed air pressure depending on the characteristic variable within the context of a closed loop control, with the actual compressed air pressure being detected by a compressed air pressure sensor.
The invention is based on the object of specifying a method for metering a reagent into an exhaust gas duct and a device for carrying out the method, the method and device permitting as exact a metering of the reagent as possible in order to avoid both metering of excessive quantities and metering of insufficient quantities.